Allergic contact dermatitis (ACD) is one of the most common and costly health problems in industrialized countries. Currently more than 100,000 chemicals are in commercial use and another 2,000 new chemicals and numerous new-product formulations are tested or marketed every year. Epicutaneous exposure to these chemicals could induce undesirable immunological skin reactions such as ACD. Although various in vivo animal models are used to evaluate potential allergenicity, these tests are subjective, time-consuming, and expensive. Therefore, an economic, in vitro predictive assay system that utilizes cells of human origin would find broad commercial utility. Various researchers have shown the critical role of dendritic cells (DC) in the initial steps of ACD such as priming naive T-cells (TC) to allergens. Here we propose an in vitro assay that utilizes a subset of dendritic cells to induce TC proliferation in predictive tests for ACD as a replacement for the local lymph node assay (LLNA). Versus the LLNA, the proposed assay is advantageous in that it utilizes cells of human origin and it eliminates the use of radioisotopes to model the primary and secondary immune responses involved in ACD. This research will develop a highly sensitive, nonanimal assay, which will be a cost-effective and accurate means of identifying contact allergens. Allergic contact dermatitis, in vitro allergenicity testing, plasmacytoid DC, myeloid DC.